Nitrogen or nitrogen/hydrogen atmospheres are used in many heat treating systems. It is important that oxygen not be present in the heat treating atmosphere as this will have a deleterious effect on the articles being treated. One way of providing a nitrogen or nitrogen/hydrogen stream into a heat treating furnace which is free of oxygen is to provide pure nitrogen, or mix pure hydrogen with pure nitrogen, produced by the cryogenic separation of air, and pass this stream to the heat treating system. While this method is effective, it is also quite expensive.
Nitrogen having a modest oxygen concentration can be produced at somewhat lower cost using non-cryogenic air separation methods such as adsorption or membrane separation systems. The oxygen is removed by reacting it with hydrogen in a catalytic reactor to form water. Excess hydrogen is used to establish a nitrogen/hydrogen stream if such is desired. However, such systems operate efficiently only at flowrates exceeding about 10,000 standard cubic feet per hour (SCFH) because for small systems having capacities less than about 10,000 SCFH, the advantages of using relatively inexpensive impure nitrogen are nullified by the expense of the deoxo system. Typical heat treating systems have atmosphere flowrate requirements within the range of from 1,000 to 8,000 SCFH.
Accordingly, it is an object of this invention to provide a system for economically producing an oxygen-free nitrogen stream, which can optionally contain hydrogen, and which can operate efficiently at flowrates less than 10,000 SCFH.